Vesicular Stomatitis Virus (VSV) is a non-segmented negative-stranded RNA virus and belongs to the family Rhabdoviridae, genus Vesiculovirus. Its simple structure and rapid high-titered growth in mammalian and many other cell types has made it a preferential tool for molecular and cell biologists in the past 30 years. This was even strengthened with the establishment of the reverse genetics system for VSV (Schnell et al., 1996).
Viral Hemorrhagic Fever (VHF) viruses are prototypes of emerging/re-emerging pathogens. Infections are serious public health concerns not just in endemic, developing countries, but also in many non-endemic developed countries. Some of them represent a threat to the world's population and thus are listed on the category A list for bioterrorism agents. The high level of biological containment needed for their manipulation has impeded studies on viruses, such as Lassa virus, Marburg and Ebola viruses, in the past. Although these viruses can be grown in tissue culture, virus propagation is usually slow and titres are low compared with other viral pathogens.
While there are no worldwide licensed vaccines for the containment level IV viruses there has been a recent report that non-human primates were protected from Ebola infection by a DNA/adenovirus immunization (Sullivan et al., 2000). This vaccine strategy required several injections of naked DNA to both the glycoprotein (GP) and nucleoprotein (NP) of Ebola virus followed by injection of adenovirus expressing the gene for Ebola GP. However, the non-human primate protective vaccine required multiple doses of naked DNA and adenovirus boost to achieve protection and in Ebola, virus dose used to challenge the monkeys was only 6 plaque-forming units, which is very low. In general, the use of this vaccine to rapidly respond to outbreaks or bio-terrorist events is limited because it requires 8 weeks just to complete the immunization schedule.
Reverse genetics systems, such as the VSV (Schnell et al., 1996), may offer a chance to overcome some of the limitations and may actually be useful to study early steps of replication such as virus entry in the context of a viral particle. Different pseudotype systems have already been used to study the role of the Ebola virus glycoprotein in cell entry (Takada et al., 1997; Wool-Lewis, 1998; Yang et al., 2000). However, the use of pseudotype particles is limited to a single step infection and, thus, remains artificial. Recombinant viruses would be more realistic and powerful to study the role during replication in vitro and in vivo. The capability of the VSV genome to tolerate additional transcription units/genes makes this system suitable for high-level expression of foreign proteins. It is relatively uncomplicated in handling and, in general, virological approaches are easily applicable.
The goal of our study was to produce recombinant VSV particles expressing transmembrane and soluble glycoproteins derived from high containment viruses with the idea to study their role in virus replication, viral pathogenesis and induction of the host immune response. Here we describe the generation of several recombinant VSV particles and the characterization of their biological phenotype.